Known in the art are MHD devices, comprising a duct for a conducting gas to flow at an angle with the direction of magnetic field induction vector, said duct being situated in the magnetic system. The duct is provided with a plurality of electrodes electrically interacting with the above gas. The working space of the duct is cross-sectionally bounded by a closed convex surface. The cross-sectional shape of the duct working space exerts substantial influence upon the output characteristics of the MHD device.
Thus, ducts having a circular cross sectional shape are known for use in MHD generators of the Faraday and frame type generators. Such ducts feature practically minimized hydraulic losses. From the viewpoint of utilization of the magnetic field volume, circular ducts are used optimally with cylindrical-shaped superconducting magnetic systems. However, combination of circular ducts with rectangular magnetic systems, such as those with an iron core, proves to be ineffective due to an incomplete utilization of the magnetic field volume.
Another type of duct is known to have its working space bounded by a rectangular contour. Such a duct has been used, in particular, in the frame-type MHD generator (cf., e.g., U.S. Pat. No. 3,387,150 dated 1968).
Ducts with rectangular cross-sectional shape of the working space provide for maximum utilization of the magnetic field volume in magnetic systems incorporating an iron core with a rectangular magnet gap.
However, rectangular-shape ducts feature an increased turbulance of the flow of gas occurring at the corners thereof within the region of the order of a local thickness of the boundary layer, which results, firstly, in unfavorable temperature distribution near the duct walls and, secondly, in increased thermohydraulic losses. Altered temperature distribution at the duct corners leads to a badly affected distribution of the conductivity of the gas working fluid, whereby a great proportion of the working current passes to the corner zones, whereas current distribution over the electrode towards the outer magnetic field becomes substantially nonuniform. In its turn, non-uniform current distribution increases the likelihood for the electrode to change over from a favorable diffusion mode of operation to an arc-shaped one, which increases by several orders of magnitude an erosion wear on the surfaces of the MHD-generator duct which in turn reduces the service life of the latter to an inadmissibly low value.